In this heat exchanger, the some of the contents of the stream leaving the bottom of T- 301 entering to E-902 are vaporized and returned to the column. The amount returned to the column is equal to the amount in Stream 10. The temperature of these streams is the boiling point of ethylbenzene at the column pressure. The heat required may be estimated by the heat of vaporization of each component at the boiling point of ethylbenzene at column pressure. There is a cost for the amount of steam needed to provide energy to vaporize the stream; this is a utility cost. The steam temperature must always be higher than the temperature of the stream being vaporized.